diff --git a/packages/core/src/telemetry/file-exporters.test.ts b/packages/core/src/telemetry/file-exporters.test.ts
new file mode 100644
index 0000000000..80a2ccafad
--- /dev/null
+++ b/packages/core/src/telemetry/file-exporters.test.ts
@@ -0,0 +1,191 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import {
+  FileSpanExporter,
+  FileLogExporter,
+  FileMetricExporter,
+} from './file-exporters.js';
+import { ExportResultCode } from '@opentelemetry/core';
+import type { ReadableSpan } from '@opentelemetry/sdk-trace-base';
+import type { ReadableLogRecord } from '@opentelemetry/sdk-logs';
+import type { ResourceMetrics } from '@opentelemetry/sdk-metrics';
+import { AggregationTemporality } from '@opentelemetry/sdk-metrics';
+import * as fs from 'node:fs';
+
+function createMockWriteStream(): {
+  write: ReturnType<typeof vi.fn>;
+  end: ReturnType<typeof vi.fn>;
+} {
+  return {
+    write: vi.fn((_data: string, cb: (err?: Error | null) => void) => cb()),
+    end: vi.fn((cb: () => void) => cb()),
+  };
+}
+
+let mockWriteStream: ReturnType<typeof createMockWriteStream>;
+
+vi.mock('node:fs', () => ({
+  createWriteStream: vi.fn(),
+}));
+
+describe('FileSpanExporter', () => {
+  let exporter: FileSpanExporter;
+
+  beforeEach(() => {
+    mockWriteStream = createMockWriteStream();
+    vi.mocked(fs.createWriteStream).mockReturnValue(
+      mockWriteStream as unknown as fs.WriteStream,
+    );
+    exporter = new FileSpanExporter('/tmp/test-spans.log');
+  });
+
+  it('should export spans successfully', () => {
+    const span = {
+      name: 'test-span',
+      kind: 0,
+      spanContext: () => ({
+        traceId: 'abc123',
+        spanId: 'def456',
+        traceFlags: 1,
+      }),
+      status: { code: 0 },
+      attributes: { key: 'value' },
+      startTime: [0, 0],
+      endTime: [1, 0],
+      duration: [1, 0],
+      events: [],
+      links: [],
+    } as unknown as ReadableSpan;
+
+    const resultCallback = vi.fn();
+    exporter.export([span], resultCallback);
+
+    expect(resultCallback).toHaveBeenCalledWith({
+      code: ExportResultCode.SUCCESS,
+      error: undefined,
+    });
+    expect(mockWriteStream.write).toHaveBeenCalledTimes(1);
+    const writtenData = mockWriteStream.write.mock.calls[0][0] as string;
+    expect(writtenData).toContain('test-span');
+  });
+
+  it('should handle circular references without crashing', () => {
+    // Simulate the circular reference structure found in OTel spans
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const span: any = {
+      name: 'circular-span',
+      kind: 0,
+      status: { code: 0 },
+      attributes: {},
+    };
+    // Create circular reference similar to BatchSpanProcessor2 -> BindOnceFuture -> _that
+    span._processor = { _shutdownOnce: { _that: span._processor } };
+    span._processor._shutdownOnce._that = span._processor;
+
+    const resultCallback = vi.fn();
+    exporter.export([span as ReadableSpan], resultCallback);
+
+    expect(resultCallback).toHaveBeenCalledWith({
+      code: ExportResultCode.SUCCESS,
+      error: undefined,
+    });
+
+    const writtenData = mockWriteStream.write.mock.calls[0][0] as string;
+    expect(writtenData).toContain('[Circular]');
+    expect(writtenData).toContain('circular-span');
+  });
+
+  it('should report failure on write error', () => {
+    const writeError = new Error('disk full');
+    mockWriteStream.write.mockImplementation(
+      (_data: string, cb: (err?: Error | null) => void) => cb(writeError),
+    );
+
+    const span = { name: 'test' } as unknown as ReadableSpan;
+    const resultCallback = vi.fn();
+    exporter.export([span], resultCallback);
+
+    expect(resultCallback).toHaveBeenCalledWith({
+      code: ExportResultCode.FAILED,
+      error: writeError,
+    });
+  });
+});
+
+describe('FileLogExporter', () => {
+  beforeEach(() => {
+    mockWriteStream = createMockWriteStream();
+    vi.mocked(fs.createWriteStream).mockReturnValue(
+      mockWriteStream as unknown as fs.WriteStream,
+    );
+  });
+
+  it('should export logs with circular references', () => {
+    const exporter = new FileLogExporter('/tmp/test-logs.log');
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const log: any = { body: 'test-log', severityNumber: 9 };
+    log.self = log;
+
+    const resultCallback = vi.fn();
+    exporter.export([log as ReadableLogRecord], resultCallback);
+
+    expect(resultCallback).toHaveBeenCalledWith({
+      code: ExportResultCode.SUCCESS,
+      error: undefined,
+    });
+
+    const writtenData = mockWriteStream.write.mock.calls[0][0] as string;
+    expect(writtenData).toContain('[Circular]');
+    expect(writtenData).toContain('test-log');
+  });
+});
+
+describe('FileMetricExporter', () => {
+  beforeEach(() => {
+    mockWriteStream = createMockWriteStream();
+    vi.mocked(fs.createWriteStream).mockReturnValue(
+      mockWriteStream as unknown as fs.WriteStream,
+    );
+  });
+
+  it('should export metrics with circular references', () => {
+    const exporter = new FileMetricExporter('/tmp/test-metrics.log');
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    const metrics: any = {
+      resource: { attributes: { service: 'test' } },
+      scopeMetrics: [],
+    };
+    metrics.self = metrics;
+
+    const resultCallback = vi.fn();
+    exporter.export(metrics as ResourceMetrics, resultCallback);
+
+    expect(resultCallback).toHaveBeenCalledWith({
+      code: ExportResultCode.SUCCESS,
+      error: undefined,
+    });
+
+    const writtenData = mockWriteStream.write.mock.calls[0][0] as string;
+    expect(writtenData).toContain('[Circular]');
+    expect(writtenData).toContain('test');
+  });
+
+  it('should return CUMULATIVE aggregation temporality', () => {
+    const exporter = new FileMetricExporter('/tmp/test-metrics.log');
+    expect(exporter.getPreferredAggregationTemporality()).toBe(
+      AggregationTemporality.CUMULATIVE,
+    );
+  });
+
+  it('should resolve forceFlush', async () => {
+    const exporter = new FileMetricExporter('/tmp/test-metrics.log');
+    await expect(exporter.forceFlush()).resolves.toBeUndefined();
+  });
+});
diff --git a/packages/core/src/telemetry/file-exporters.ts b/packages/core/src/telemetry/file-exporters.ts
index 55fe641035..def6e91f44 100644
--- a/packages/core/src/telemetry/file-exporters.ts
+++ b/packages/core/src/telemetry/file-exporters.ts
@@ -17,6 +17,7 @@ import type {
   PushMetricExporter,
 } from '@opentelemetry/sdk-metrics';
 import { AggregationTemporality } from '@opentelemetry/sdk-metrics';
+import { safeJsonStringify } from '../utils/safeJsonStringify.js';
 
 class FileExporter {
   protected writeStream: fs.WriteStream;
@@ -26,7 +27,7 @@ class FileExporter {
   }
 
   protected serialize(data: unknown): string {
-    return JSON.stringify(data, null, 2) + '\n';
+    return safeJsonStringify(data, 2) + '\n';
   }
 
   shutdown(): Promise<void> {